1. Electric Resistance Welding
Welds of the type suggested in this application were generally accomplished by means of electric resistance-welding techniques. In these methods, electrodes are applied to the weld zone with pressure in order to compress the overlapping layers of metal in the weld zone. By applying electric power to the electrodes current flows across the joint through the overlapping metal layers. Since the resistance is high at the interface of the layers, welding temperatures may be achieved and a weld nugget is formed at the joint.
The weld therefore is interior to the layers and cannot be visually inspected. One example of a test which is used to inspect the integrity of the resistance-welded joint for quality control is the "peel" test. In this test, a sample of the workpiece is joined by a single spot utilizing the same procedures as applied in a production operation for a finished part. After welding, one side of the joined sample is clamped and the other is peeled off. The weld button may then be examined to determine the parameters of the fused zone. Although this information may then be applied to the production cycle, it is clear that an accurate correlation depends on the ability to accurately control and monitor the operation. Since this method of welding is used for large volume, repetitive, production work in which one machine can be set up to make thousands of similar joints, close control and monitoring of the conditions of the weld zone are not always possible. The operator is, therefore, required to take frequent samples and perform the destructive "peel" test.
The disadvantages of resistance-welding, apart from the difficulty of inspection and process control, are that it requires a high heat input which creates thermal distortions on the workpiece.
2. Laser Welding
Welding operations utilizing a laser beam as the energy source are becoming more prevalent in the production environment. A laser beam is an intense, highly coherent beam of monochromatic light which has been amplified many times. Since the beam is exceptionally intense, extremely narrow and highly coherent, it may be focussed to an image that is brighter than the original source. In this way it is possible to obtain a light source so intense it can fuse steel and other metals to form a weld. The beam may also be optically deflected for accurate placement of the weld zone. The use of inert gas shielding in the work zone will improve the quality of the weld.
Similar to electron beam techniques, laser welding provides deeper penetration and is very suitable for delicate work. It is also a rapid, precise and highly controllable process which creates exceptionally high quality welds. A laser welding process generally requires less heat input than resistance-welding with a reduction in distortion.
It is the purpose of this invention to provide a welding process utilizing a laser which is as simple and repeatable as a resistance-weld process and creates a high strength weld that may be easily inspected.